Method for the manufacture of heterogeneous penetration compound metal

ABSTRACT

In a protective gas atmosphere, at least one metal of high vapor pressure (diffusion metal) is admitted as an alloying component through diffusion into the impregnating metal of lower melting point such as silver or copper contained in the pores of the frame metal, such as tungsten, rhenium or molybdenum. The diffusion temperature is chosen so that the impregnating metal exists in the liquid phase at least after the diffusion of the diffusion metals. The diffusion takes place, preferably, at 20 to 240*C above the melting temperature of the impregnating metal or the alloy formed between the impregnating metal and the diffusion metal. As the diffusion metal is used at least one of the metals bismuth, cadmium, gallium, indium, lead, tin and tellurium.

finite States Patent 1191 Hassler et a1.

Siemens Aktiengesellschaft, M1L11911213I11 ansilit en sn, Germany Filed:Dec. 28, 1971 Appl. No.: 213,205

Assignee:

Foreign Application Priority Data Jan. 13, 1971 u.s.c1...-. 117/227,117/99, 117/131,

117/230 Int. Cl B4411 1/02 Field of Search 117/227, 131, 230, 99

References Cited UNITED STATES PATENTS 9/1958 Hoyer 117/227 Germany2101414 May 21, 1974 2,671,955 3/1954 Grubel et a1 117/131 2,813,808.11/1957 Hoyer 117/131 2,706,759 4/1955 Williamson 117/227 3,290,17012/1966 Houston 117/227 Primary ExaminerCameron K. Weiffenbach Attorney,Agent, or Firm-l-lerbert L. Lerner [5 7] ABSTRACT In a protective gasatmosphere, at least one metal of high vapor pressure (diffusion metal)is admitted as an alloying component through diffusion intothe'impregnating metal of lower melting point such as silver or coppercontained in the pores of the frame metal, such as tungsten, rhenium ormolybdenum. The diffusion temperature is chosen so that the impregnatingmetal exists in the liquid phase at least after the diffusion of thediffusion metals. The diffusion takes place, preferably, at 20 to 240Cabove the melting temperature of the impregnating metal or the alloyformed between the impregnating metal and the diffusion metal. As thediffusion metal is used at least one of the metals bismuth, cadmium,gallium, indium, lead, tin and tellurium.

6 Claims, N0 Drawings METHOD FOR THE MANUFACTURE OF IIETEROGENEOUSPENETRATION COMPOUND METAL SPECIFICATION The present invention concernsa method for the manufacture of a heterogeneous penetration compoundmetal especially for use as contact material for vacuum circuitbreakers, in which the pores ofa porous sintering skeleton of ahigh-melting, burn-off resistant metal (skeleton metal) such astungsten, rhenium or molybdenum or of an alloy of these metals, arefilled with a lower melting metal (impregnating metal) of high electricconductivity, such as silver and copper, or with a lower melting alloyof these metals.

ln contact materials which are used in vacuum circuit breakers, therequirement exists for extremely low gas content and gas producingimpurities. Such contact materials should, in addition, exhibitparticularly low weld-ability and little burn-off due to evaporation inan arc, in order to obtain long life and low contact resistance. Thelatter requirement regarding low contact resistance can easily be met ina vacuum circuit'breaker due to the fact that the chemical and physicalsubstances which are active in the atmosphere are absent,

in contrast to air circuitbreakers, and no foreign layers are generatedat the contact surfaces of compounds of the contact metals and oxygen orsulfur, respectively. Furthermore, there exists a requirement for a lowchopping effect, i.e., in switching small currents the arc should not beinterrupted so that voltage spikes which might lead to breakdowns, arecaused by the induction effect. In order to obtain this anti-choppingeffect, components which have high vapor pressure under the conditionsin the arc, are added to the basic contact material, whereby aconstriction of the arc due to current forces (pinch effect) is avoided.

The known contact materials of copper or copper alloys exhibitrelatively high weldability and great burnoff particularly when used invacuum circuit breakers.

to l,500C, if a metal with high vapor pressure is used for achieving theanti-chopping effect, it is difficult to maintain a desired definedcontent of the metal.

It is an objective of the invention to provide a method for amanufacture of the above-named contact materials, avoiding the describeddifficulties regarding maintenance of a defined content of an effectivecomponent of a metal with high vapor pressure.

We resolve this problem by adding at least one metal or a metal alloy ofhigher vapor pressure than that of the liquid copper (diffusion metal)as the alloying component by diffusion, in a protective gas atmosphere,which has low solubility in the diffusion metal and the impregnatingmetal, into the lower-melting impregnating metal located in the pores ofthe skeleton (frame) metal wherein the compound material of the skeletonmaterial and impregnating metal has already been degassed in a precedingoperation in a high vacuum. The diffusion temperature is chosen so thatthe impregnating metal exists in the liquid phase at least after thediffusion metal is diffused in.

The diffusion of the diffusion metal into the impregnating metal,filling the pores of the high melting component, takes place in theliquid state of the impregnating and diffusion metal. The diffusiontemperature is preferably 20 to 240C above the melting temperature ofthe impregnating metal or the alloy which is formed between theimpregnating metal and the diffusion metal. If silver is used asimpregnating metal, the diffusion temperatures of 1,000 to l,200C arepreferably used. If copper is used as the impregnating metal, diffusiontemperatures between 1,100 and l,300 are used.

Particularly suited as diffusion metals are at least one of the metalsbismuth, cadmium, gallium, indium, lead, tin and tellurium.

As a surprising effect, it has been found in the diffusion process thatbismuth in copper as the impregnating metal which is situated in thepores of the sintered skeleton of molybdenum or tungsten, reaches adepth of penetration of 5 mm at temperatures of l',200C after about 15minutes. After the diffusion treatment, the bismuth content in thecopper impregnated region is practically uniform within the space of thepores of the high melting component. According to this diffusion method,it is possible to distribute the diffusion metal in theimpregnationmetal with high vapor pressure in a defined,'desiredconcentration. For vacuum circut breakers, it has been foundparticularly successful to use WCuBi contact materials with coppercontents of Example 1 A contact'blank of WCu 20 with 80 g W and 20 g Cuis placed in a 35 mm diameter graphite crucible. 0.3 to L0 g of bismuthor tellurium was added as the diffusion metal. The graphite crucible wassubsequently heated to a temperature between l,l00 and 1,200C. Thediffusion took place in a protective gas atmosphere of argon or nitrogenand was completed after about 10 minutes. Subsequently, the graphitecrucible was cooled.

Example 2 In a variant of the method, an alloy, for instance of 10 g ofCu.. As a diffusion metal, 5 g of a prealloyed CuBi 4 to 12 or CuTe 4 to12 was, for instance, added. The quantity and concentration of theprealloyed material was so determined that a final concentration of 0.3to 1.0 percent by weight is obtained. Subsequently, the crucible washeated to a temperature of 1,000 to l,100C. The diffusion took placeunder a protective gas atmosphere of argon or nitrogen and was completedafter about minutes. Subsequently, the graphite crucible was cooled.

What is claimed is:

1. In the manufacture of an electrical contact comprising forming acomposite structure constituted of a porous sintered body selected fromthe group consisting of tungsten, rhenium, molybdenum and a high meltingalloy thereof, filling the pores of the sintered body with animpregnating metal selected from the group consisting of copper, silverand a low melting alloy thereof and degassing the structure in a highvacuum, wherein the improvement comprises subsequent to the degassingstep, contacting the exposed surfaces of the impregnating metal with adiffusion metal selected from the group consisting of bismuth, cadmium,gallium, indium, lead tin, tellurium and an alloy thereof in aprotective gas atmosphere which has low solubility in both theimpregnating metal and the diffusion metal, and heating the structure toa temperature of from to 240C above the melting point of theimpregnating metal or of the alloy to be formed between the impregnatingmetal and the diffusion metal for a period of time sufficient to diffusethe diffusion metal into the impregnating metal.

2. Th method of claim 1, wherein the impregnating metal is silver andthe temperature to which the structure is heated is from 1,000 to1,200(I.

3. The method of claim 1, wherein the impregnating metal is copper andthe temperature to which the structure is heated is from l,l00 to1,300C.

4. The method of claim 1, wherein bismuth is diffused into copper at atemperature of 1,200C for 15 minutes.

5. The method of claim 1, wherein the diffusion metal is an alloyselected from the group consisting of copper-bismuth andcoppentellurium.

6. The method of claim 1, wherein the protective atmosphere is. selectedfrom the group consisting of argon and nitrogen.

2. Th method of claim 1, wherein the impregnating metal is silver andthe temperature to which the structure is heated is from 1,000* to1,200*C.
 3. The method of claim 1, wherein the impregnating metal iscopper and the temperature to which the structure is heated is from1,100* to 1,300*C.
 4. The method of claim 1, wherein bismuth is diffusedinto copper at a temperature of 1,200*C for 15 minutes.
 5. The method ofclaim 1, wherein the diffusion metal is an alloy selected from the groupconsisting of copper-bismuth and copper-tellurium.
 6. The method ofclaim 1, wherein the protective atmosphere is selected from the groupconsisting of argon and nitrogen.